The Frasch process can be used to obtain sulfur from the ground wherein air and superheated water is injected into subterranean sulfur deposits to melt the sulfur and force it to the surface. Elemental sulfur may also be obtained in large quantities from hydrogen sulfide contained in petroleum refinery gas streams or wellhead gas. In the U.S., elemental sulfur is generally transported from field storage to users sites in the molten state due to environmental and specification considerations. In Canada and other parts of the world, however, molten sulfur at the field distributing plant may be pelleted or pumped onto concrete pads open to the atmosphere or into slip forms, for storage whereupon the molten sulfur solidifies into large slabs. The slabs of sulfur must either be mechanically broken up, re-liquefied, or re-liquefied and pelleted for final distribution to the consumer. The breaking-up operation is cumbersome and entails much labor and expense, and the resulting sulfur, which is extremely friable, contains a huge volume of sulfur dust or fines comprised of small particles having a high surface area which almost always cause significant environmental harm due to deposition on surrounding equipment, land and vegetation. This has led to the banning of the transport, storage and use of such xe2x80x9ccrushed bulkxe2x80x9d sulfur in many parts of the world. It is well known that molten sulfur may also be solidified into prills, granules, or pellets by the use of prilling towers, granulators, pelletizers, pastillers and the like as shown in U.S. Pat. Nos. 4,234,318 and 4,595,350, and many more similar patents. Such xe2x80x9csulfur pelletsxe2x80x9d are far easier to transport and handle in bulk than xe2x80x9ccrushed bulk,xe2x80x9d and that is the reason such types of pellets were developed. Various types of sulfur pellets are the preferred form in which most solid sulfur is transported by ocean vessel to consumers throughout the world. Despite their superiority over xe2x80x9ccrushed bulkxe2x80x9d, all types of sulfur pellets retain solid sulfur""s inherent characteristic of becoming increasingly brittle as it xe2x80x9ccuresxe2x80x9d over time. Accordingly, the handling of all sulfur pellets products in bulk can generate considerable sulfur fines, which, in turn, may cause significant environmental harm. Materials handling procedures for sulfur pellets are therefore subject to stringent requirements. The State of Florida (Rule 62-296, F.A.C), for example, requires the use of special unloading facilities and procedures, which increase both the capital and operating costs of sulfur pellet handling and storage activity, particularly when dealing with vessel unloading. As part of the Rule, Florida requires the cessation of marine unloading operations whenever wind speed at the dock exceeds 18 mph for a 5-minute period.
As is the case with any form of solid sulfur, sulfur pellets and the attendant sulfur fines can readily be contaminated with Thiobacillus thiooxidans. This bacillus generates sulfuric acid as part of its life cycle. Sulfuric acid, which often exists in sulfur pellets at concentrations that can exceed 1,000 ppm, is a contaminant which can cause severe corrosion damage to receiving and processing facilities (current industry norms on loading a vessel with sulfur pellets call for xe2x80x9cfree acidxe2x80x9d (sulfuric) not to exceed 100 ppm.) All forms of solid sulfur transported by sea run the additional risk of contamination by hydrochloric acid. Hydrochloric acid is formed by contact of sulfuric acid with seawater or salt. The presence of hydrochloric acid in solid sulfur can have truly catastrophic consequences on processing equipment, as most metals impervious to sulfuric acid are not impervious to hydrochloric acid. Therefore, large solid sulfur processing facilities receiving sea-borne sulfur incur the added cost of neutralizing such acids prior to melting the sulfur. The resultant ash waste must then be filtered from the molten sulfur stream using steam jacketed, diatomaceous earth, pressure leaf filters. This represents further capital, operating and waste disposal costs.
Shipments of solid sulfur pellets via railcars and vessels are sometimes contaminated with extraneous materials such as sand, rocks, organic and metallic materials. All of these contaminants cause processing problems, from degrading sulfur purity, frequent and costly cleanouts of filter leafs and sump pumps to breaking pump impellers.
It is known from U.S. Pat. No. 3,761,136 that sulfur can be formed into prills and transported through a pipeline by forming a slurry of sulfur prills and water and pumping the slurry through the pipeline. However, this technique also generates and transports undesirable sulfur fines.
The invention is a process and apparatus for hydraulically transporting sulfur pellets with minimal degradation of the pellets while allowing the removal of sulfur fines, extraneous impurities and the ability to neutralize acids as needed. It is comprised of the steps of pumping water from a water supply into a quantity of said sulfur pellets and sulfur fines with a jet-venturi-eductor-pumping system to produce a water slurry containing sulfur pellets and sulfur fines, pumping said water slurry with one or more rotating disk-boundary layer pumps to a series of static screens to separate from said water slurry large lumps, coarse impurities, and a sulfur fines slurry, to yield the desired sulfur pellet slurry, contacting the sulfur pellet slurry with a dewatering disk to remove substantially all the remaining water, transporting the dewatered sulfur pellets to storage, pumping the sulfur fines slurry to a hydrocyclone to separate water from the sulfur fines, recycling the recovered water to said water supply, and recovering the sulfur fines.
The apparatus comprises the combination of a first pump for pumping water from a water supply tank into a supply of sulfur pellets containing sulfur fines as a jet stream to produce a water slurry containing said sulfur pellets and sulfur fines, a second pump for pumping the water slurry upward to a series of screens with minimal disintegration of said pellets, a series of screens to separate from said water slurry large lumps and impurities, a sulfur fines slurry, and a sulfur pellet slurry, a dewatering disk to remove substantially all the remaining water from the sulfur pellet slurry, a hydrocyclone to separate substantially all the water from the sulfur fines slurry, a first tank for the recovery of said sulfur fines slurry, a third pump for pumping the sulfur fines slurry to said hydrocyclone, and a second tank for recovery of recycled water. If desired, a pH meter can be in contact with said water slurry to determine the need for additions of basic materials